A POWERFUL explosion wrecked the office of an American security company in Kabul yesterday, killing at least seven people, officials said.

The blast hit the office of Dyncorp, a private firm which protects Afghan President Hamid Karzai and works for the US government in Iraq, said Nick Downie of the Afghanistan Security Office.

Downie said he and others who rushed to the scene pulled five to six people from the building with serious injuries, including several US citizens.

"We're looking at a similar number who died, a mixture of Afghans and internationals," said Downie, a former British soldier who advises relief groups on security.

"The explosion which occurred in front of the Kabul office of an international security company killed at least seven people," Karzai's office added in a statement.

"Two Americans, three Nepalese and two Afghan nationals, including a child, have been confirmed dead."

The blast was in the Shar-e Naw district of Kabul, an area with offices of international organisations and guesthouses used by their staff.

The building was burning fiercely after the explosion. Windows were blown out of surrounding houses.

Residents said a cobbler, whose stall was blown away by the blast, was also killed, and up to eight others wounded.

"It was a very, very big explosion, and there were a lot of injured," said Ahmad Emal, a young shopkeeper watching behind the police cordon.

The charred wreckage of a car was also visible in front of the house. Afghans crowded round what appeared to be the engine block several hundred yards away, suggesting the explosion might have been caused by a car-bomb.

"There was a crater right in front of the office door," Downie said. "There's not much doubt about the target."

Security officials have issued several warnings in recent weeks of possible car-bomb and suicide attacks in the Afghan capital.

Nato forces who patrol the capital have warned that anti-government militants, including the ousted Taleban, could try to mount spectacular attacks in a bid to disrupt forthcoming elections.

Officials from the international force could not be reached for comment.

On Saturday night an explosion ripped through a school in south-eastern Afghanistan, killing nine children and one adult, the US military said.

An Afghan official said the blast in Paktia province was caused by a bomb, though the military said it was still unclear.

"There was an explosion, that's all we know," American spokeswoman Master Sgt. Ann Bennett said. "Killed were four children, five teenagers and one adult."

An eight-year-old boy injured in the blast was taken to an American military base for treatment, Bennett said.

Paktia governor Asadullah Wafa said eight children aged seven to 15 were killed and 15 other people injured, three of them critically. It was not clear if two had subsequently died of their wounds.

The American military said it was helping local authorities investigate the explosion, which Bennett said occurred as the children were attending an evening class.

The Mullah Khel school near Zormat, about 80 miles south of the capital, Kabul, was an Islamic school which also taught the more modern syllabus set by the Afghan Education Ministry.

It received funding from an international aid group, Wafa said, something that could have made it a target for Taleban-led militants.